#include<stdio.h>
#include<math.h>
void main(){
    double max(double x, double y);
    double x, y, z;
    printf("please input two double numbers: \n");
    scanf("%f %f", &x, &y);
    z = max(x,y);
    printf("max is: %f",z);
}

double max(double x, double y){
    if(x >= y){
        return x;
    }else{
        return y;
    }
}